Electrical means for mechanical rectifiers to limit contact wear



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Eau/4x0 daf/v .051cm rro JENSEN April 28, 1959 E. J. DIEBOLD ET AL ELECTRICAL MEANS FOR MECHANICAL RECTIFIERS TO LIMIT CONTACT WEAE Filed Nov. l2. 1954 5 Sheets-Sheet 5 81.00/ (2 /n/LL/sfc) Trae/VPS@ United States Patent ELECTRICAL MEANS FOR MECHANICAL RECTIFIERS TO LIMIT CONTACT WEAR Edward John Diebold, Ardmore, and Otto Jensen, Malvern, Pa., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application November 12, 1954, Serial No. 468,380 Claims. (Cl. 321-48) Our present invention relates to electrical means for mechanical rectifiers to limit contact wear and more particularly is directed toward a novel arrangement whereby the voltage across the main cooperating contacts is maintained at Zero magnitude immediately prior to contact engagement.

Experiments have demonstrated that the voltage existing across cooperating contacts immediately prior to the contact engagement have resulted in contact erosion, loss of contact atness and therefore loss of proper timing of the cooperating contacts.

The following test indicated that contact wear occurred during contact make rather than during contact break: A pair of cooperating contacts A and B were connected in parallel across a common source and were provided with driving means to cause the set of contacts A to make or engage prior to the set of contacts B and to cause contacts B to disengage or break prior to the disengagement of the set of contacts A. By this experiment it was possible to separate the make duty and the break duty of the contacts and it was found that the make contacts (set A) were badly eroded and damaged whereas the break contacts (set B) had little or no sign of wear.

When a mechanical rectifier is operated at maximum D.C. output voltage, the source voltage and current are in phase and the cooperating contacts engage when there is little or no voltage difference between the contacts as they approach each other. Therefore, little or no contact wear is experienced when the rectifier is operated under these conditions.

However, when the device is operated with a relatively low D.C. output voltage, the source current is shifted With respect to the source voltage and thus the cooperating contacts make at a later time within the cycle when there is a voltage difference therebetween which results in undesirable erosion. Thus, the more the D.-C. voltage is decreased by means of phase control, the greater will be the voltage dilerence between the cooperating contacts during make and hence, the greater the erosion. That is, as a result of the contact voltage, as the cooperating contacts are being moved to make position, material is transferred from one contact to another and to the surrounding atmosphere.

It is a primary object of our invention to provide a novel auxiliary circuit whereby the voltage across the cooperating contacts is substantially reduced immediately prior to contact engagement.

Another object of our invention is to provide a novel auxiliary circuit to control the pre-excitation winding of the main make commutating reactor so that the voltage across the main cooperating contacts will be at substantially zero magnitude during the contact make step.

These and other objects of our invention will become apparent when taken in connection with the drawings in which:

Figure 1 is' a schematic three phase wire diagram of a prior art mechanical rectifier.

2,884,585 Patented Apr. 28, 1959 Figure 2A is a voltage versus time representation illustrating the voltage across the main cooperating contacts of the rectifier of Figure 1 when this unit is adjusted for full output voltage. This figure illustrates the zero voltage across the main cooperating contacts immediately prior to contact engagement.

Figure 2B is a current versus time representation illustrating the current through the main cooperating contacts of the rectifier of Figure 1 when this unit is adjusted for full output voltage.

Figure 3A is a voltage versus time representation illustrating the voltage across the main cooperating contacts of the rectifier of Figure 1 when this unit is adjusted for reduced output voltage. This figure illustrates the relatively large magnitude of voltage which exists across the main cooperating contacts immediately prior to contact engagement.

Figure 3B is a current versus time representation illustrating the current through the main cooperating contacts of the rectifier of Figure l when this unit is adjusted for reduced output voltage.

Figure 4 is a schematic three phase wire diagram of a mechanical rectifier having a common commutating reactor for the positive and negative main contacts and illustrates our novel auxiliary circuit comprised of an auxiliary make commutating reactor and auxiliary cooperating contacts.

Figure 5 is a schematic wire diagram illustrating the manner in which the control winding of the auxiliary make reactor of Figure 4 can energize from an independent A.C. source through a variac and selenium rectiher.

Figure 5A is a current versus time representation illustrating the energizing current for the control winding of the auxiliary make reactor as controlled by a selenium rectifier.

Figure 6 is a schematic wire diagram of one phase of a mechanical rectifier illustrating a second embodiment of my invention.

Figure 7 is a schematic three-phase wire diagram of a one Way mechanical rectifier and illustrates our novel electrical control circuit applied to phase C.

Figure 8 is a hysteresis loop for a make reactor illustrating dynamic and static conditions.

Figure 1 shows a schematic wire diagram, of a three phase priorart mechanical rectifier having a source of power supplying the primary windings 11 of the three phase transformer 10. The secondary windings 12 are respectively connected to phases A, B, C each of which contain a main make commutating reactor 13, break comrnutating reactor 14 and cooperating positive and negative contacts 15 and 16, respectively. The main winding 17 of the comrnutating reactor 1S is connected in series with each pair of cooperating contacts 15 and 16. The cooperating contacts 15 and 16 may have the construction and be controlled as shown in co-pending applications Serial No. 301,880, filed luly 3l, 1952, now Patent No. 2,759,128; Serial No. 307,024, filed August 29, 1952, now Patent No. 2,845,592; Serial No. 307,067, filed August 29, 1952, now Patent No. 2,798,909; Serial No. 331,467, filed January 15, 1953, now Patent No. 2,759,141, all assigned to the assignee of the instant application.

The commutating reactor 18 may be controlled by preexcitation and flux reversal circuits as illustrated in copending application Serial No. 423,357, filed April 15, 1954, now Patent No. 2,860,301 and Serial No. 423,358, filed April l5, 1954, now Patent No. 2,817,805.

The coordination of the plurality of cooperating contacts 1 5 and 16 permits the rectification of the A.C. source supplying the primary winding 11 to provide ,D.C. output voltage for the load 19.

Figures 2A and 2B show the voltage and current conditions which exist within the rectier when the phase control is adjusted for maximum D.C. output Voltage. Thus, for example, the make step which occurs between the time t1 and t3 exists when the supply voltage is passing through zero value. That is, since it is desired to obtain the maximum D.C. output voltage, the source current and voltage are in phase and the cooperating contacts are closed early in the voltage cycle to obtain this maximum output Voltage. Thus, as seen in Figure 2B the cooperating contacts will close during the period t2 and t3 of the make step and therefore as best seen in 'Figure 2A, the voltage across the cooperating contacts will be zero or substantially zero during contact make. Hence, there will not be any erosion or damage of the contacts.`

However, when the mechanical rectilier is adjusted for reduced D.C. output voltage by means of shifting the phase of the current with respect to the voltage, the make step will exist between the times t4 and t5, as best seen in Figure 3B. Since the time t., occurs within the cycle after the supply voltage has passed through zero into the positive half cycle, there will be voltage across the main cooperating contacts immediately prior to contact make as seen in Figure 3A.

Thus, when the main cooperating contacts 15 are being closed the voltage which exists at the time l., will be applied thereacross, thereby resulting in the corrosion and transfer of contact material.

Figure 4 shows a three phase mechanical rectilier with the auxiliary circuit of our invention applied thereto. The diagram of Figure 4, except for the addition of our novel auxiliary electrical circuit is similar to the wiring diagram of Figure l and identical components are identied by similar numerals.

Each of the phases A, B and C are provided with our novel auxiliary circuit in order to reduce the voltage on the main cooperating contact immediately prior to contact engagement. The auxiliary circuit is as follows:

The auxiliary make reactor 2@ is provided with a main Winding 21 which is connected in series with positive auxiliary contacts 22. One of the cooperating auxiliary contacts 22 is connected directly to the main winding 21 and the other is connected to the load side of the main contact 15. The auxiliary make reactor 20 is also provided with a control winding 23 which is energized and controlled as illustrated in Figures and 6 and will hereinafter be more fully described.

The circuit comprising the auxiliary make reactor 20 and the auxiliary cooperating contacts 22 are provided to protect the positive main cooperating contacts 15. A similar circuit being comprised of the auxiliary make reactor 30 and the negative auxiliary cooperating contacts 32, is provided for the negative main cooperating contacts 16.

The main windings 21 and 31 of the auxiliary make reactors 20 and 3), respectively, are connected together in series with the make pre-excitation coil 40 of the main make commutating reactor 13. The opposite end of the make pre-excitation coil 40 is connected to the main line which comprises the main winding 17, the commutating reactor 1S.

It will be noted that the auxiliary circuitry above described is provided for each of the phases A, B and C of the mechanical rectifier.

The auxiliary contacts 22 and 32 may be driven by synchronous means in substantially the same manner as the main contact 15 and 16. The driving means for the auxiliary contacts 22 and 32 is synchronized with the driving means for the main contacts 15 and 16 so that the auxiliary contacts make or close prior to their associated main contacts. Thus, for example, the auxiliary contacts 22 make before the main contact 15 and the auxiliary contacts 32 make before its associated main contacts 16. In addition to this synchronization the auxiliary contacts 22, 32 will mechanically close whenever the supply voltage is passing through zero. That is, the auxiliary contacts 22 are adjusted to make at voltage zero and to break later.

The main cooperating contacts 15 will make after its associated auxiliary contacts 22 and will be separated whenever it is required for desirable commutation and operation. It will be noted that since the control coil 23 of the auxiliary make reactor 20 is supplied from a separate and independent source that the step of the auxiliary make reactor 20 can be adjusted to any desirable length. The operation of the circuit is as follows:

After the auxiliary contacts 22 have been driven closed, the current will commence to flow from the secondary winding 12 through the make pre-excitation coil 413, through the main winding 21 of the auxiliary make reactor 2t), through the auxiliary contacts 22, through load 19, through the main cooperating contact of an adjacent phase (for example contact 16 in phase C) and then back to the winding of the transformer associated with that phase.

Initially the auxiliary make reactor 20 is unsaturated so that its main winding 21 has an iniinite impedance to thereby create a make step for the auxiliary contacts 22.

It will be noted that the step current owing through the auxiliary circuit comprised of the auxiliary make reactor 20 and the auxiliary contacts 22 is very small and hence will not cause any flux change in the main make reactor 13. However, since the auxiliary make reactor 22 is not saturated, a flux change will take place in the core thereof and hence full voltage will appear across its main winding 21, as above noted.

However, when the core of the auxiliary make reactor 20 becomes fully saturated the main winding 21 will no longer limit the small magnitude of step current and therefore the current will increase to the magnitude of step current and therefore the current will increase to the magnitude of the step current for the main make reactor 13. That is, since the main make reactor 13 is unsaturated at the time, its pre-excitation coil 40 will limit the curre-nt ow through the auxiliary circuit. At the moment the auxiliary make reactor 20 becomes saturated, thereby resulting in an increase in the current ow therethrough to the magnitude of step current for the make reactor 13, the voltage across the main winding 21 decreases to substantially zero and the source voltage will now appear across the make pre-excitation coil 40 of the main make reactor 12. That is, the voltage which previously appeared across the main winding 21 of the auxiliary make reactor 20 will collapse and will thereafter exist across the make pre-excitation coil 40 of the main make reactor 13. By means of transformer action this voltage appearing across the make pre-excitation coil 40 will also appear across the main winding 17 of the main make reactor 13. The pre-excitation coil 40 and the main winding 17 are constructed with the same number of turns so that the voltage appearing on each of the windings due to transformer action will be equal.

Since one of the main cooperating contacts 15 is connected to the main coil 17 and the other of the main cooperating contacts 15 is now eifectively connected to one end of the pre-excitation coil 4t), and since these two windings have an equal magnitude of voltage thereon, the voltage existing across the main cooperating contacts 15 will be zero. That is, even though the load voltage may have existed across the main cooperating contacts 15 while they were separated a maximum distance, the voltage thereacross immediately prior to contact engagement will suddenly collapse to zero thereby preventing any possibility of contact erosion or transfer of contact material.

It will be noted that our novel circuit not only reduces the voltage across the cooperating contacts during make to a zero value but also automatically adjusts the preexcitation current of the make'reactor 13 to the dynamic value and therefore the inrush current through the main contacts 22 Will be zero.

There is a difference in the width of the magnetization loop lbetween static and dynamic conditions and since it has heretofore been impossible to pre-excite the making reactor with current corresponding to the dynamic lloop, it has previously been impractical to design the make reactor for a short step. That is, when the commutating reactor is suddenly magnetized, a high voltage appears across it and the ux changes very rapidly.

The rapid change in flux induces eddy current in the iron laminations which distort the shape of the hysteresis loop and hence, increases the magnetizing current. The fast and slow magnetization is illustrated in Figure 8.

A change from one speed to the other, as for example when voltage changes suddenly, means a rapid increase in current, as illustrated by the horizontal dotted line.

With our novel circuit, the voltage immediately prior to contact closing and immediately afterwards are identical and hence, the speed of magnetization remains constant before and after. Therefore the magnetizing current remains constant and no sudden change of current will fiow through the contacts.

Thus, the addition of the auxiliary make reactor 20 automatically adjusts the pre-excitation current to the dynamic value so that the inrush current through contacts will be zero. Hence, the actual step between the contact make and end of lche make step can now be made shorter and therefore the power factor can be improved.

1t is during the period of time after the auxiliary contacts 22 have closed and following the saturation of the auxiliary make reactor tlhat the main cooperating contacts 15 are mechanically closed; that is, during the period of time when the voltage across the main cooperating contacts is zero. At the time the main cooperating contacts 15 are closed, a parallel path through the above described auxiliary circuit exists. However, the auxiliary circuit comprised of the make pre-excitation coil 40, the main winding 2l and the auxiliary contacts 22 is highly reactive, 'so that the step current which was previously flowing therethrough will continue to flow therethrough and the main make reactor 13 will continue to generate its make step, as long as it remains unsaturated. After the main make reactor 13 is completely saturated the main current from the secondary winding 12 will divide through the path containing the main cooperating contacts 15 and the auxiliary cooperating contacts 22. However, the auxiliary path is designed to have a relatively high resistance in comparison to the main path comprised of the main winding 17 and the main cooperating contacts 15, so that a relatively small percentage of the total load current will flow through the auxiliary circuit. This arrangement is specifically provided so that the auxiliary contacts can be open on a relatively small magnitude of current without the necessity of providing a break reactor therefor.

That is, since the magnitude of current owing through the auxiliary circuit is relatively small it is not necessary to provide a break step in order to protect the auxiliary contacts.

In Figure 5 we have lshown the energizing circuit for the control winding of the auxiliary make reactor. It will be noted that in Figure 5 we have shown the auxiliary make reactor 2t) which is associated with the positive main cooperating contacts 15. However, it will now be apparent that the auxiliary make reactor Sti, which is associated with the negative main cooperating contacts 16, has a similar control and energizing circuit. Thus, as seen in Figure 5A separate A.C. source 24 is provided to energize the variac 25. T he output of the variac is adjusted by means 26 which is supplied through the` selenium rectifier 27 to energize the control winding 20 of the auxiliary make reactor 23.

The circuitry comprised of the variac 25 and selenium rectifier 27 provides proper flux reversal for the auxiliary drive the auxiliary contacts 22 and 32.

make reactor 23. That is, after the closing ofthe auxiliary contacts 22 it is possible to start the reversing of the flux in the auxiliary make reactor 20 so that this reactor will be prepared to perform its duty on the next closing operation of its associated auxiliary contacts.

The selenium rectifier 27 is poled in the control circuit of the control winding 23 to prevent the energization thereof during the conducting period of its associated auxiliary contacts 22. Thus, as seen in Figure 5A during the positive half cycle of the A.C. source 24 there will be no current ow through the control winding 23 of the auxiliary make reactor 20, i.e. the period of time that the auxiliary contacts 22 are closed.

When the auxiliary contacts 22 are open, the selenium rectifier 27 will permit the energization of the control winding 23 and hence a ux reversal will take place within the core of the auxiliary make reactor 20.

When the adjustment means 26 of the variac 25 is positioned for maximum voltage on the control winding 23 a complete reversal of the flux in the auxiliary make reactor 20 is achieved. Thus, upon the closing of the auxiliary contacts 22 the auxiliary make reactor 20 is completely saturated in the opposite direction for current flow in the main winding 21 thereof, and hence a maximum step is produced by auxiliary make reactor 20.

When a minimum or low voltage is applied to the control winding 23 of the auxiliary make reactor 20 there will be no reversal of flux therein and hence no step will be provided by the auxiliary make reactor 20. It will be noted that since an independent energizing circuit is provided for the control winding 23 of the auxiliary make reactor 20 the length or period of time of the make step is completely independent of the make step of the main reactor 13.

Hence, when the mechanical rectifier is operated for maximum D.C. output voltage (that is, the make step occurring very early within the voltage cycle) the variac 25 will be adjusted to supply substantially high voltage to the control winding 23 so that no step will occur. However, when the mechanical rectifier is phase shifted so that D.C. output voltage is at a minimum value the variac 25 is adjusted by means 26 to have a maximum voltage applied to the control winding 23 so that the step period for the auxiliary make reactor 20 will be at a maximum.

It will be noted that automatic means can be provided to adjust the unit 26 so that control winding 23 will be energized by a magnitude of voltage which will be a function of the magnitude of D.C. output voltage.

As seen in Figure 6 a common source of supply 24 may be provided to energize both the positive auxiliary make reactor 2t) and the negative auxiliary make reactor 30. However, the rectifier 37 for the control Winding 33 will be poled in an opposite direction to the rectifier 27 since their respective auxiliary make reactors 20 and 30 function on alternate halves of the cycle.

In Figure 6 we have also shown a second embodiment of our invention whereby the auxiliary contacts are replaced by means of selenium rectiiers. Thus, for example, the selenium rectifier 42 will replace the positive auxiliary cooperating contacts 22 and a selenium rectifier 52 Will replace the negative auxiliary cooperating contacts 32.

As heretofore noted, mechanical means are provided to However, by replacing the auxiliary contacts by means of selenium rectifiers 42, 52, these units will be controlled by the magnitude of source voltage. Since they are poled in opposite directions, they will alternately permit current to flow therethrough in substantially the same function as heretofore described in Figure 4.

Figure 6 also illustrates an advantage which may be achieved by our novel auxiliary circuit. It is desirable to connect an R-C circuit in parallel with the main cooperating contacts of a mechanical rectifier in order to adjust contact opening. Thus, for example, the capacitor 60 is connected in series with the resistor 61 and the series combination connected in parallel with the cooperating contacts 15.

When the contact 15 opens, it will carry a small residual current which produces a high recovery voltage if there is no low impedance bypass. Thus, an R-C circuit 60-61 is provided as a spark extinguisher bypass.

However, in the prior art arrangement, the R-C circuit could not be used since the condenser 60 is charged by the voltage which exists across the cooperating contacts 15 and would then suddenly discharge through the main contacts 15 thereby causing an undue wear of these contacts. That is, without an auxiliary make reactor 20, the condenser 60 would charge and discharge during part of the make step of the main cooperating contacts 15 immediately prior to contact closing.

However, with our novel auxiliary circuit wherein the voltage across the main cooperating contacts is collapsed prior to the engagement of the contacts, the condenser will not be charged and hence, will not be able to damage the contacts by discharge.

It will be noted that our novel circuitry can be applied to many of the various electrical circuits which are used for mechanical rectiers. Thus, it could be used in the multiple two-phase single-way mechanical rectifier circuit described in copending application or in the six phase halt' wave mechanical rectier circuit described in copending application Serial No. 361,669, led June 15, 1963.

In Figure 7, we have illustrated the manner in which our novel circuit can be applied to a one way rectifier. For simplicity, corresponding components are marked with identical numbers as heretofore used and described in connection with Figures 4, and 6.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention within the scope of the description herein are obvious. Accordingly, we prefer to be bound not by the specific disclosures herein by only by the appending claims.

We claim:

l. In a mechanical rectifier for energizing a D.-C. load from an A.C. source; said mechanical rectier comprising a make reactor and a pair of main cooperating contacts; said make reactor having a main winding and a pre-excitation winding; said pair of main cooperating contacts being operated into and out of engagement in synchronism with the frequency of said A.C. source; said A.C. source make reactor main winding, pair of main cooperating contacts and D.C. load being connected in series; an auxiliary circuit; said auxiliary circuit Ecomprising an auxiliary make reactor and a switching means; said auxiliary make reactor having a main winding; said A.C. source, pre-excitation winding, auxiliary make reactor main Winding, switching means and D.C. load being connected in series; said switching means 4being constructed to pass current through said auxiliary circuit and effect saturation of said auxiliary make reactor prior to contact closure of said main cooperating contacts to thereby induce flux reversal in said make reactor prior to contact closure of said main cooperating contacts.

2. In a mechanical rectifier for energizing a D.-C. load from an A.C. source; said mechanical rectier comprising a make reactor and a pair of main cooperating contacts; said make reactor having a main winding and a preexcitation winding; said pair of main cooperating contacts being operated into and out of engagement in synchronism with the frequency of said A.C. source; said A.C. source, make reactor main winding, pair of main cooperating contacts and D.C. load being connected in series; an auxiliary circuit; said auxiliary circuit comprising an auxiliary make reactor and a switching means; said auxiliary make reactor having a main winding; said A.C. source, pre-excitation winding, auxiliary make reactor main winding, switching means and D.C. load being connected in series; said switching means being constructed to pass current through said auxiliary circuit and effect saturation of said auxiliary make reactor prior to contact closure of said main cooperating contacts to thereby induce ilux reversal in said make reactor prior to contact closure of said main cooperating contacts; said auxiliary circuit collapsing the voltage across said main contacts where said auxiliary make reactor is saturated and prior to the time said contacts are engaged.

3. In a mechanical rectifier for energizing a D.-C. load from an A.C. source; said mechanical rectifier cornprising a make reactor and a pair of main cooperating contacts; said make reactor having a main winding and a pre-excitation winding; said pair of main cooperating contacts being operated into and out of engagement in synchronism with the frequency of said A.C. source; said A.C. source, make reactor main winding, pair of main cooperating contacts and D.C. load being connected in series; an auxiliary circuit; said auxiliary circuit comprising an auxiliary make reactor and a switching means; said auxiliary make reactor having a main winding and a control winding; said A.C. source, pre-excitation winding, auxiliary make reactor main winding, switching means and D.C. load being connected in series; said switching means being constructed to pass current through said auxiliary circuit and eect saturation of said auxiliary make reactor prior to contact closure of said main cooperating contacts to thereby induce flux reversal in said make reactor prior to contact closure of said main cooperating contacts; said auxiliary circuit collapsing the voltage across said main contacts where said auxiliary make reactor is saturated and prior to the time said contacts are engaged; said control winding being energized from an A.C. source to adjustably control the point of saturation of said auxiliary make reactor.

4. In a mechanical rectifier for energizing a D.C. load from an A.C. source; said mechanical rectifier comprising a make reactor and a pair of main cooperating contacts; said make reactor having a main winding and a pre-excitation winding; said pair of main cooperating contacts being operated into and out of engagement in synchronism with the frequency of said A.C. source; said A.C. source, make reactor main winding, pair of main cooperating contacts and D.C. load being connected in series; an auxiliary circuit; said auxiliary circuit comprising an auxiliary make reactor and a switching means; said auxiliary make reactor having a main Winding and a control Winding; said A.C. source, pre-excitation winding, auxiliary make reactor main winding, switching means and D.-C. load being connected in series; said switching means being constructed to pass current through said auxiliary circuit and effect saturation of said auxiliary make reactor prior to contact closure of said main cooperating contacts to thereby induce flux reversal in said make reactor prior to contact closure of said main cooperating contacts where said auxiliary make reactor is saturated and prior to the time said contacts are engaged; said control winding being energized from an auxiliary A.C. source; said auxiliary A.C. source energizing said control winding through an adjustable voltage means and a rectilier7 said adjusted voltage means providing a minimum step length when the output voltage of said mechanical rectifier is at a minimum and a maximum make step length, when the output voltage of said mechanical rectifier is at maximum.

5. In a mechanical rectifier for energizing a D.C. load from an A.C. source; said mechanical rectifier comprising a make reactor and a pair of main cooperating contacts; said make reactor having a main winding and a pre-excitation Winding; said pair of main cooperating contacts being operated into and out of engagement in synchronism with the frequency of said A.C. source; said A.C. source, make reactor main winding, pair of assigns main cooperating contacts and D.C. load being connected in series; an auxiliary circuit; said auxiliary circuit comprising an auxiliary make reactor and a switching means; said auxiliary make reactor having a main winding and a control winding; said A,C. source; pre-excitation winding, auxiliary make reactor main winding, switching means and D.C. load being connected in series; said switching means being constructed to pass current through said auxiliary circuit and effect saturation of said auxiliary make reactor prior to contact closure of said main cooperating contacts to thereby induce flux reversal in said make reactor prior to contact closure of said main cooperating contacts; said auxiliary circuit collapsing the voltage across said main contacts where said auxiliary make reactor is saturated and prior to the time said contacts are engaged; said control winding being energized from an auxiliary A.C. source energizing said control 10 winding through an adjustable voltage means and a rectitier; said auxiliary A.C. source, said adjusted voltage means, said rectiiier and said control winding serving as a flux reversal circuit for said auxiliary make reactor.

References Cited in the file of this patent UNITED STATES PATENTS 2,610,231 Wettstein Sept. 9, 1952 2,756,381 Rolf July 24, 1956 2,771,577 Kesselring Nov. 20, 1956 FOREIGN PATENTS 506,015 Great Britain May 22, 1939 874,202 France July 31, 1942 229,786 Switzerland Feb. 16, 1944 915,587 Germany July 26, 1954 299,072 Switzerland Aug. 2, 1954 

